It is desirable to make the dimensions of the initial cut around the vent of the bird as small as possible so that the "plug" of material removed contains only a minimal amount of edible meat. On the other hand, it is necessary to thereafter enlarge this entryway into the cavity because its dimensions are too small to permit the entry of a tool for removing the viscera within the cavity. Consequently, it has long been the practice to manually slit the skin between the vent hole and the keel bone of the bird so as to provide an opening of the requisite dimensions without sacrificing edible portions of the bird.
Various efforts have been made to automate this enlarging or "opening" step, but none has heretofore been entirely successful for a number of reasons. Included among these is the fact that many prior opening mechanisms have simply been unduly complicated. Additionally, many have been unable to satisfactorily make the opening cut without also puncturing or otherwise unintentionally damaging the organs disposed closely beneath the skin intended to be severed. The latter type of mishap results in spewing contaminated fluids over the otherwise edible portions of the bird to the end that the entire bird may be unfit for consumption. Examples of method and apparatus to overcome these prior shortcomings are disclosed and claimed in prior copending application, titled "Method and Apparatus for Opening the Body Cavity of Poultry," Ser. No. 835,671, filed Sept. 22, 1977, in the names of Scheier, et al., and assigned to the assignee of the present invention.
While the arrangement described and claimed in the aforesaid application has indeed proven to be a significant improvement over prior opening methods and machines, it has been found that by limiting the extent to which the slitting knife can move in a certain direction corresponding to its depth of insertion into the hole of the bird, the actual depth of insertion can vary depending upon the particular length of the bird being processed. In other words, the knife in the aforesaid application is not adjustable relative to the length of each bird it encounters, and instead comes to a certain fixed position each and every operation, regardless of whether the bird is long or short. Hence, it is possible that the knife might be inserted more deeply into short birds than long ones, since both are suspended by their hocks from an overhead conveyor. Excessive depth of penetration of the knife could result in accidental puncture of the intestines and other organs containing contaminants that would spoil the meat.
It is known in the art to associate the slitting knife with a special locating carriage that does not permit operation of the knife until such time as the carriage has reached and engaged the stern of the bird, whatever its length. Once the stern has been engaged, the knife can move through its predetermined slitting movements with the assurance that the same depth of penetration will be achieved regardless of the length of the bird.